The standard model’s greatest triumph
The standard model predicts the electron magnetic moment to an astonishing accuracy of one part in a trillion.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
SEARCH · Search NASA
Results for “STANDARD MODEL OF PARTICLE PHYSICS”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Almost inert Higgs bosons at the LHC
Non-minimal Higgs sectors are strongly constrained by the agreement of the measured couplings of the 125 GeV Higgs with Standard Model predictions. This agreement can be explained by an approximate $\mathbb{Z}_{2}$ symmetry under which the additional Higgs bosons are odd. This allows the additional Higgs bosons to be approximately inert, meaning that they have suppressed VEVs and suppressed mixing with the Standard Model Higgs. In this case, single production of the new Higgs bosons is suppressed, but electroweak pair production is unsuppressed. We study the phenomenology of a minimal 2 Higgs doublet model that realizes this scenario. In a wide range of parameters, the phenomenology of the model is essentially fixed by the masses of the exotic Higgs bosons, and can therefore be explored systematically. We study a number of different plausible signals in this model, and show that several LHC searches can constrain or discover additional Higgs bosons in this parameter space. We find that the reach is significantly extended at the high luminosity LHC.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Partially natural two Higgs doublet models
It is possible that the electroweak scale is low due to the fine-tuning of microscopic parameters, which can result from selection effects. The experimental discovery of new light fundamental scalars other than the Standard Model Higgs boson would seem to disfavor this possibility, since generically such states imply parametrically worse fine-tuning with no compelling connection to selection effects. We discuss counterexamples where the Higgs boson is light because of fine-tuning, and a second scalar doublet is light because a discrete symmetry relates its mass to the mass of the Standard Model Higgs boson. Our examples require new vectorlike fermions at the electroweak scale, and the models possess a rich electroweak vacuum structure. Furthermore, the mechanism that we discuss does not protect a small CP-odd Higgs mass in split or high-scale supersymmetry-breaking scenarios of the MSSM due to an incompatibility between the discrete symmetries and holomorphy.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Electroweak Phase Transition with Spontaneous $Z_2$-Breaking
This work investigates a simple, representative extension of the Standard Model with a real scalar singlet and spontaneous $Z_2$ breaking, which allows for a strongly first-order phase transition, as required by electroweak baryogenesis. We perform analytical and numerical calculations that systematically include one-loop thermal effects, Coleman-Weinberg corrections, and daisy resummation, as well as evaluation of bubble nucleation. We study the rich thermal history and identify the conditions for a strongly first-order electroweak phase transition with nearly degenerate extrema at zero temperature. This requires a light scalar with mass below 50 GeV. Exotic Higgs decays, as well as Higgs coupling precision measurements at the LHC and future collider facilities, will test this model. Additional information may be obtained from future collider constraints on the Higgs self-coupling. Gravitational-wave signals could potentially be probed by future gravitational wave experiments.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Classical and quantum discrete dynamical systems
We study deterministic and quantum dynamics from a constructive “finite” point of view, since the introduction of the continuum or other actual infinities in physics poses severe conceptual and technical difficulties, and while all of these concepts are not really needed in physics, which is in fact an empirical science. Particular attention is paid to the symmetry properties of discrete systems. For a consistent description of the symmetries of dynamical systems at different time instants and the symmetries of various parts of such systems, we introduce discrete analogs of gauge connections. These gauge structures are particularly important to describe the quantum behavior. The symmetries govern the fundamental properties of the behavior of dynamical systems. In particular, we can show that the moving soliton-like structures are inevitable in a deterministic (classical) dynamical system, whose symmetry group breaks the set of states into a finite number of orbits of the group. We demonstrate that the quantum behavior is a natural consequence of symmetries of dynamical systems. This behavior is a result of the fundamental inability to trace the identity of indistinguish-able objects during their evolution. Information is only available on invariant statements and values related with such objects. Using general mathematical arguments, any quantum dynamics can be shown to reduce to a sequence of permutations. The quantum interferences occur in the invariant subspaces of permutation representations of the symmetry groups of dynamical systems. The observables can be expressed in terms of permutation invariants. We also show that in order to describe quantum phenomena it is sufficient to use cyclotomic fields—the minimal extensions of natural numbers suitable for quantum mechanics, instead of a non-constructive number system—the field of complex numbers. The finite groups of symmetries play the central role in this review. In physics there is an additional reason for such groups to be of interest. Numerous experiments and observations in particle physics point to the importance of finite groups of relatively low orders in a number of fundamental processes. The origin of these groups has no explanation within presently recognized theories, such as the Standard Model.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Enhancing sensitivities to long-lived particles with high granularity calorimeters at the LHC
The search for long-lived particles (LLP) is an exciting physics opportunity in the upcoming runs of the Large Hadron Collider. In this paper, we focus on a new search strategy of using the High Granularity Calorimeter (HGCAL), part of the upgrade of the CMS detector, in such searches. In particular, we demonstrate that the high granularity of the calorimeter allows us to see “shower tracks” in the calorimeter, and can play a crucial role in identifying the signal and suppressing the background. We study the potential reach of the HGCAL using a signal model in which the Standard Model Higgs boson decays into a pair of LLPs, h → XX. After carefully estimating the Standard Model QCD and the misreconstructed fake-track backgrounds, we give the projected reach for both an existing vector boson fusion trigger and a novel displaced-track-based trigger. Our results show that the best reach for the Higgs decay branching ratio, BR(h → XX), in the vector boson fusion channel is about O(10 –4 ) with lifetime cτ X ~ 0.1–1 meters, while for the gluon gluon fusion channel it is about O(10 –5 – 10 –6 ) for similar lifetimes. For longer lifetime cτ X ~ 103 meters, our search could probe BR(h → XX) down to a few ×10 –4 (10 –2 ) in the gluon gluon fusion (vector boson fusion) channels, respectively. In comparison with these previous searches, our new search shows enhanced sensitivity in complementary regions of the LLP parameter space. We also comment on many improvements can be implemented to further improve our proposed search.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for dark matter in events with a hadronically decaying W or Z boson and missing transverse momentum in p p collisions at s = 8 TeV with the ATLAS detector
CERN-LHC. A search is presented for dark matter pair production in association with a W or Z boson in pp collisions representing 20.3 fb^-1 of integrated luminosity at sqrt(s) = 8 TeV using data recorded with the ATLAS detector in 2012 at the Large Hadron Collider. Events with a hadronic jet with the jet-mass consistent with a W or Z boson, and with large missing transverse momentum are analyzed. The data are consistent with the Standard Model expectations, and limits are set on the mass scale in effective field theories that describe the interaction of dark matter and Standard Model particles.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
A clockwork solution to the flavor puzzle
We introduce a set of clockwork models of flavor that can naturally explain the large hierarchies of the Standard Model quark masses and mixing angles. Since the clockwork only contains chains of new vector-like fermions without any other dynamical fields, the flavor constraints allow for relatively light new physics scale. For two benchmarks with gear masses just above 1 TeV, allowed by flavor constraints, we discuss the collider searches and the possible ways of reconstructing gear spectra at the LHC. We also examine the similarities and differences with the other common solutions to the SM flavor puzzle, i.e., with the Froggatt-Nielsen models, where we identify a new clockworked version, and with the Randall-Sundrum models.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Flavoured axions in the tail of B q → μ+μ- and B → γ* form factors
We discuss how LHC di-muon data collected to study B q → μμ can be used to constrain light particles with flavour-violating couplings to b -quarks. Focussing on the case of a flavoured QCD axion, a , we compute the decay rates for B q → μμa and the SM background process B q → μμγ near the kinematic endpoint. These rates depend on non-perturbative B q → γ (*) form factors with on- or off-shell photons. The off-shell form factors — relevant for generic searches for beyond-the-SM particles — are discussed in full generality and computed with QCD sum rules for the first time. This includes an extension to the low-lying resonance region using a multiple subtracted dispersion relation. With these results, we analyse available LHCb data to obtain the sensitivity on B q → μμa at present and future runs. We find that the full LHCb dataset alone will allow to probe axion-coupling scales of the order of 10 6 GeV for both b → d and b → s transitions. As a spin-off application of the off-shell form factors we further analyse the case of light, Beyond the Standard Model, vectors.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Nonstandard Yukawa couplings and Higgs portal dark matter
We study the implications of non-standard Higgs Yukawa couplings to light quarks on Higgs-portal dark matter phenomenology. Saturating the present experimental bounds on up-quark, down-quark, or strange-quark Yukawa couplings, the predicted direct dark matter detection scattering rate can increase by up to four orders of magnitude. The effect on the dark matter annihilation cross-section, on the other hand, is subleading unless the dark matter is very light — a scenario that is already excluded by measurements of the Higgs invisible decay width. We investigate the expected size of corrections in multi-Higgs-doublet models with natural flavor conservation, the type-II two-Higgs-doublet model, the Giudice-Lebedev model of light quark masses, minimal flavor violation new physics models, Randall-Sundrum, and composite Higgs models. We find that an enhancement in the dark matter scattering rate of an order of magnitude is possible. In conclusion, we point out that a discovery of Higgs-portal dark matter could lead to interesting bounds on the light-quark Yukawa couplings.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
New measurements on physics of B-hadrons in ATLAS experiment
Recent results on B-hadron physics in ATLAS are reviewed. A new measurement of CP-violating parameters in B{sub s }→ J/ψφ decay is performed on full Run 1 statistics. Branching fraction BR(B{sub s }→ μ{sup +}μ{sup −}) = (0.9{sup +1.1}{sub −0.8} )×10{sup −9} is measured, below the Standard Model (SM) prediction.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Little Conformal Symmetry
We explore a new class of natural models which ensure the one-loop divergences in the Higgs mass are cancelled. The top-partners that cancel the top loop are new gauge bosons, and the symmetry relation that ensures the cancellation arises at an infrared fixed point. Such a cancellation mechanism can, a la Little Higgs models, push the scale of new physics that completely solves the hierarchy problem up to 5-10 TeV. When embedded in a supersymmetric model, the stop and gaugino masses provide the cutoffs for the loops, and the mechanism ensures a cancellation between the stop and gaugino mass dependence of the Higgs mass parameter.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Electroweak precision observables and Higgs-boson signal strengths in the Standard Model and beyond: present and future
We present results from a state-of-the-art fit of electroweak precision observables and Higgs-boson signal-strength measurements performed using 7 and 8 TeV data from the Large Hadron Collider. Based on the HEPfit package, our study updates the traditional fit of electroweak precision observables and extends it to include Higgs-boson measurements. As a result we obtain constraints on new physics corrections to both electroweak observables and Higgs-boson couplings. We present the projected accuracy of the fit taking into account the expected sensitivities at future colliders.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Two Higgs doublet model with vectorlike leptons and contributions to pp → W W and H → W W
In this paper, we study a two Higgs doublet model extended by vectorlike leptons mixing with one family of standard model leptons. Generated flavor violating couplings between heavy and light leptons can dramatically alter the decay patterns of heavier Higgs bosons. We focus on pp → H → ν 4 ν μ → W μν μ , where ν 4 is a new neutral lepton, and study possible effects of this process on the measurements of pp → W W and H → W W since it leads to the same final states. We discuss predictions for contributions to pp → W W and H →WW and their correlations from the region of the parameter space that satisfies all available constraints including precision electroweak observables and from pair production of vectorlike leptons. Large contributions, close to current limits, favor small tan β region of the parameter space. We find that, as a result of adopted cuts in experimental analyses, the contribution to pp → W W can be an order of magnitude larger than the contribution to H → W W . Thus, future precise measurements of pp → W W will further constrain the parameters of the model. Also, we also consider possible contributions to pp → W W from the heavy Higgs decays into a new charged lepton e 4 (H → e 4 μ → W μν μ ), exotic SM Higgs decays, and pair production of vectorlike leptons.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
The Higgs and leptophobic force at the LHC
The Higgs boson could provide the key to discover new physics at the Large Hadron Collider. We investigate novel decays of the Standard Model (SM) Higgs boson into leptophobic gauge bosons which can be light in agreement with all experimental constraints. We study the associated production of the SM Higgs and the leptophobic gauge boson that could be crucial to test the existence of a leptophobic force. Our results demonstrate that it is possible to have a simple gauge extension of the SM at the low scale, without assuming very small couplings and in agreement with all the experimental bounds that can be probed at the LHC.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Signals of the electroweak phase transition at colliders and gravitational wave observatories
If the electroweak phase transition (EWPT) is of strongly first order due to higher dimensional operators, the scale of new physics generating them is at the TeV scale or below. In this case the effective-field theory (EFT) neglecting operators of dimension higher than six may overlook terms that are relevant for the EWPT analysis. In this article we study the EWPT in the EFT to dimension eight. We estimate the reach of the future gravitational wave observatory LISA for probing the region in which the EWPT is strongly first order and compare it with the capabilities of the Higgs measurements via double-Higgs production at current and future colliders. Furthermore, we also match different UV models to the previously mentioned dimension-eight EFT and demonstrate that, from the top-down point of view, the double-Higgs production is not the best signal to explore these scenarios.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
A tale of twin Higgs: natural twin two Higgs doublet models
In original twin Higgs model, vacuum misalignment between electroweak and new physics scales is realized by adding explicit Z 2 breaking term. Introducing additional twin Higgs could accommodate spontaneous Z 2 breaking, which explains origin of this misalignment. We introduce a class of twin two Higgs doublet models with most general scalar potential, and discuss general conditions which trigger electroweak and Z 2 symmetry breaking. Various scenarios on realising the vacuum misalignment are systematically discussed in a natural composite two Higgs double model framework: explicit Z 2 breaking, radiative Z 2 breaking, tadpole-induced Z 2 breaking, and quartic-induced Z 2 breaking. Finally, we investigate the Higgs mass spectra and Higgs phenomenology in these scenarios.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Baryonic Higgs at the LHC
We investigate the possible collider signatures of a new Higgs in simple extensions of the Standard Model where baryon number is a local symmetry spontaneously broken at the low scale. Here, we refer to this new Higgs as “Baryonic Higgs”. This Higgs has peculiar properties since it can decay into all Standard Model particles, the leptophobic gauge boson, and the vector-like quarks present in these theories to ensure anomaly cancellation. We investigate in detail the constraints from the γγ, Zγ, ZZ, and W W searches at the Large Hadron Collider, needed to find a lower bound on the scale at which baryon number is spontaneously broken. The di-photon channel turns out to be a very sensitive probe in the case of small scalar mixing and can severely constrain the baryonic scale. Finally, we also study the properties of the leptophobic gauge boson in order to understand the testability of these theories at the LHC.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗